The present invention relates to a process for producing particles which comprise at least one halogen-free flame retardant and which comprise at least one metal oxide or semimetal oxide, where the particle can be a core-shell particle with flame retardant in the core and metal oxide or semimetal oxide in the shell, or a particle in which the distribution of flame retardant and metal oxide or semimetal oxide is in essence homogeneous. The present invention further relates to particles comprising at least one halogen-free flame retardant and comprising at least one metal oxide or semimetal oxide, to a polymer molding composition comprising said particles and comprising at least one thermoplastic or thermoset polymer, and also to the use of said particles in polymer molding compositions or for providing flame retardancy to polymer molding compositions.
Composite materials comprising flame retardants and comprising other materials are known in the prior art.
PMSE Preprints (2008), 98, 533 to 535 discloses microcapsules which have a core-shell structure. Tris(2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane-1-oxo-4-methanol) phosphate (trimer), is present as flame retardant within the core of said microcapsules. A melamine resin forms the shell of these microcapsules.
JP 2000263733 discloses a process for impregnating fibrous substrates with phenolic-resin lacquers which comprise microcapsules comprising phosphates.
Donghua Daxue Xuebao, Ziran Kexue Ban (2007), 33(6), 701 to 705, discloses core-shell particles comprising water-soluble dimethyl methylphosphonate (DMMP) as core material and the product of acetalization of PVA and GA (glutaraldehyde) as shell material, obtainable via an emulsion process.
The prior art does not disclose any particles which comprise a halogen-free, preferably water-insoluble, flame retardant in combination with at least one metal oxide or semimetal oxide, for example SiO2, TiO2 and/or ZnO. There is moreover no disclosed process in which, for example, silica is formed via a sol-gel process.